U.S. patent application number 10/342505 was filed with the patent office on 2003-07-24 for print media heating techniques for a vacuum belt hard copy apparatus.
Invention is credited to Elgee, Steven B., Medin, Todd R., Rasmussen, Steve O., Wotton, Geoff.
Application Number | 20030137573 10/342505 |
Document ID | / |
Family ID | 24355956 |
Filed Date | 2003-07-24 |
United States Patent
Application |
20030137573 |
Kind Code |
A1 |
Rasmussen, Steve O. ; et
al. |
July 24, 2003 |
Print media heating techniques for a vacuum belt hard copy
apparatus
Abstract
A print media preheating method and apparatus uses heat, vacuum,
and mechanisms for drying and flattening a sheet prior to ink-jet
printing thereon. Pre-shrinking the media, driving out and
substantially reducing inherent moisture content prior to
depositing wet ink thereon provides greater flatness in the
print-zone whereby ink-jet print quality is improved.
Inventors: |
Rasmussen, Steve O.;
(Vancouver, WA) ; Wotton, Geoff; (Battleground,
WA) ; Elgee, Steven B.; (Portland, OR) ;
Medin, Todd R.; (Vancouver, WA) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY
Intellectual Property Administration
P. O. Box 272400
Fort Collins
CO
80527-2400
US
|
Family ID: |
24355956 |
Appl. No.: |
10/342505 |
Filed: |
January 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10342505 |
Jan 14, 2003 |
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09588941 |
Jun 6, 2000 |
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6536894 |
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Current U.S.
Class: |
347/104 |
Current CPC
Class: |
B41J 11/0024 20210101;
B41J 11/0085 20130101; B41J 11/002 20130101 |
Class at
Publication: |
347/104 |
International
Class: |
B41J 002/01 |
Claims
What is claimed is:
1. A method for flattening print media prior to ink-jet printing
thereon, comprising steps of: heating the print media over a
predetermined time and temperature such that moisture content is
substantially reduced prior to printing thereon; and pressing the
print media upstream of printing thereon.
2. The method as set forth in claim 1, comprising the step of:
heating the print media at least prior to pressing.
3. The method as set forth in claim 2, comprising the step of:
continuing the heating during the pressing.
4. The method as set forth in claim 1, comprising the step of:
applying a vacuum force to the print media during said
pressing.
5. The method as set forth in claim 4, further comprising the step
of: using said vacuum force to assist pressing the print media
between pressing members.
6. A subsystem for an ink-jet hard copy apparatus, having a
belt-type print media transport means for transporting print media
via a vacuum belt along a media path through a print zone of the
apparatus, the subsystem comprising: upstream of the print zone,
media transporting means for transporting print media along the
path toward the print zone, the media transporting means including
at least two complementary contact devices wherein the print media
has each face thereof in contact with a respective device surface;
and heating means for heating at least one of the contact devices
surface such that heat is transferred to the print media
therefrom.
7. The subsystem as set forth in claim 6, the media transporting
means comprising: a section of the vacuum belt located at any
instant of time upstream of the print zone, and a separate contact
belt mounted in the apparatus adjacently to the vacuum belt in said
print media path, such that the surfaces of the vacuum belt and
contact belt are in contact at the section of the vacuum belt
upstream of the print zone.
8. The subsystem as set forth in claim 7, comprising: the contact
belt is non-perforated.
9. The subsystem as set forth in claim 8, comprising: the
non-perforated belt is vacuumed against the perforated belt,
helping to press the medium therebetween.
10. The subsystem as set forth in claim 6, the media transporting
means comprising: a pair of belts mounted in the apparatus in the
print media path upstream of the vacuum belt wherein the heating
means heats at least one surface of one of the belts of the
pair.
11. The subsystem as set forth in claim 10, further comprising:
upstream of said print zone and in contact with the vacuum belt,
media retaining means for receiving a leading edge of the print
media from the pair of belts.
12. The subsystem as set forth in claim 11, comprising: the media
retaining means and vacuum belt contact is such that a
predetermined degree of buckling of the media is induced along the
print media path between the media transporting means and the media
retaining means point of contact with the vacuum belt.
13. The subsystem as set forth in claim 12, comprising: wherein
said pair of belts run at a first speed, up to and including a
constant speed, said media retaining means runs at a second speed
associated with printing on the media, and said first speed and
said second speed are associated to form the degree of
buckling.
14. The subsystem as set forth in claim 10, comprising: one of said
belts is a perforated vacuum belt and the other of said belts is a
non-perforated belt wherein the pair of belts are in surface
contact such that the non-perforated belt is pulled against the
perforated vacuum belt.
15. A method for pretreating an ink-jet print medium sheet prior to
printing thereon in an ink-jet hard copy apparatus, comprising the
steps of: pressing the sheet between a pair of print media
transport devices in the print media transport path prior to
printing on the media; moving the sheet with the devices toward a
printing-zone of the apparatus; and heating a surface of at least
one device of the pair of devices such that heat is transferred to
the sheet substantially immediately prior to depositing ink
thereon.
16. The method as set forth in claim 15, the step of pressing
further comprising: vacuum-assisted pressing of the print
media.
17. The method as set forth in claim 15, comprising the further
step of: actively removing vapors produced by the heating of the
sheet.
18. An ink-jet hard copy apparatus, comprising: an ink-jet writing
instrument positioned adjacently to a printing-zone in a print
media transport path of the apparatus; a vacuum belt subsystem for
receiving a sheet of print media, including a vacuum belt for
transporting the sheet through the printing-zone; and upstream of
the printing-zone, a preheating subsystem having a media transport
mechanism and a heater mechanism associated with the media
transport mechanism wherein heat is applied by the preheating
subsystem to at least one surface of the sheet prior to the sheet
entering the printing-zone and receiving colorant from the writing
instrument.
19. The apparatus as set forth in claim 18, comprising: the
preheating subsystem incorporates a region of the vacuum belt
upstream of the printing-zone at any given time during transport of
the sheet along the print media transport path.
20. The apparatus as set forth in claim 18, the media transport
mechanism comprising: a secondary, non-perforated, belt in contact
with the vacuum belt upstream of the printing-zone such that the
sheet has opposite surfaces thereof pressed against surfaces of the
vacuum belt and the secondary belt, respectively, when transported
along the print media transport path upstream of the
printing-zone.
21. The apparatus as set forth in claim 20, comprising: contact
between the belts is vacuum forced.
22. The apparatus as set forth in claim 18, comprising: the region
of the vacuum belt is associated with the heater mechanism such
that heat is imparted to the sheet on the region and vacuum draws
vapor from the sheet from the region.
23. The apparatus as set forth in claim 20, comprising: the heater
mechanism is associated with the secondary belt.
24. The apparatus as set forth in claim 20, comprising: the heater
mechanism is associated with both the vacuum belt and the secondary
belt such that each belt has a heated surface and the opposite
surfaces of the sheet are both heated by the preheating
subsystem.
25. The apparatus as set forth in claim 18, the preheating
subsystem, comprising: upstream in the print media path of the
vacuum belt, a pair of print media contact belts for feeding the
sheet therebetween along the path from an upstream preheating
subsystem input side to a downstream preheating subsystem output
side proximate the vacuum belt wherein the heater mechanism is
associated with at least one of the contact belts.
26. The apparatus as set forth in claim 25, comprising: a pinch
roller associated with the vacuum belt proximate the output side of
the preheating subsystem upstream of the print-zone.
27. The apparatus as set forth in claim 26, comprising: the pinch
roller and vacuum belt receive a leading edge of the sheet in a
roller-belt interface therebetween within the preheating subsystem
and are controlled such that a predetermined buckling of the sheet
is formed between the preheating subsystem output side and the
roller-belt interface such that the sheet is positioned with
respect to the printing-zone by the pinch roller and vacuum
belt.
28. The apparatus as set forth in claim 26, comprising: the pinch
roller and vacuum belt receive a leading edge of the sheet in a
roller-belt interface therebetween while upstream regions of the
sheet are still within the preheating subsystem.
29. The apparatus as set forth in claim 18, comprising: the heater
mechanism provides a region for pre-heating region for heating the
sheet prior to the sheet entering a nip between a belt for driving
the media through the printing-zone and a device for pressing the
media against the belt.
30. The apparatus as set forth in claim 18, the preheating
subsystem comprising: the belt is a vacuum belt for transporting
the sheet through the printing-zone, a compliant material pressing
mechanism is in contact with the belt upstream of the
printing-zone, forming a nip the sheet must pass through upstream
of the printing-zone; and the heater mechanism drives moisture from
the sheet prior to the sheet entering the nip.
31. A print media ironing device for ink-jet printers having a
vacuum transport belt for moving a sheet of print media through a
print-zone, comprising: at least one heater providing a
pre-shrinkage region wherein the sheet passing therethrough
experiences a substantial moisture content reduction; and at least
one ironing mechanism, downstream of said region, wherein the sheet
is pressed into a substantially planar configuration prior to
entering the print-zone.
32. The device as set forth in claim 31, further comprising: said
heater further provides heat to the sheet while the sheet is
pressed.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to ink-jet printing
and, more specifically, to vacuum belt-type ink-jet printers and
the utilization of multiple belts and associated devices for
heating and pressing print media.
[0003] 2. Description of Related Art
[0004] The art of ink-jet technology is relatively well developed.
Commercial products such as computer printers, graphics plotters,
copiers, and facsimile machines employ ink-jet technology for
producing hard copy. The basics of this technology are disclosed,
for example, in various articles in the Hewlett-Packard Journal,
Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39,
No. 5(October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6
(December 1992) and Vol. 45, No.1 (February 1994) editions. Ink-jet
devices are also described by W. J. Lloyd and H. T. Taub in Output
Hardcopy [sic ] Devices, chapter 13 (Ed. R. C. Durbeck and S.
Sherr, Academic Press, San Diego, 1988). [For convenience of
describing ink-jet technology and the present invention, all types
of print media are referred to simply as "paper," all compositions
of colorants are referred to simply as "ink," and all types of hard
copy apparatus are referred to simply as a "printer" No limitation
on the scope of invention is intended nor should any be
implied.]
[0005] FIG. 1 (PRIOR ART) depicts a generic, vacuum belt print
media transport, ink-jet hard copy apparatus, in this exemplary
embodiment a computer peripheral, ink-jet printer 10. An ink-jet
writing instrument 12 (also referred to hereinafter as simply a
"pen") is provided with a printhead 14 having drop generators (not
seen in this view), including nozzles for ejecting ink droplets
onto an adjacently positioned print medium, e.g., a sheet of paper
16, in the apparatus' printing-zone 34. An endless-loop belt 32 is
one type of known manner printing-zone input-output paper
transport. A motor 33 having a drive shaft 30 is used to drive a
gear train 35 coupled to a belt pulley 38 mounted on a fixed axle
39; a known manner position tracking device 41 can be provided. A
biased idler wheel 40 provides appropriate tensioning of the belt
32. The belt rides over a platen 36 in the print-zone 34. The
platen 36 is associated with a known manner vacuum induction system
37. The paper sheet 16 is picked from an input supply (not shown)
and its leading edge 54 is delivered to a guide 50, 52 where a
pinch wheel 42 in contact with the belt 32 --or the belt vacuum
force itself --grips the leading edge of the sheet to continue
transport of the paper sheet 16 through the printing-zone 34 (the
paper path is represented by arrow 31). Downstream of the
printing-zone 34, an output roller 44 in contact with the belt 32
receives the leading edge 54 of the paper sheet 16 and continues
the paper transport until the trailing edge 55 of the now printed
page is released; in some implementations, suction force release is
sufficient for allowing the sheet to leave the printing-zone 34
transport mechanisms. A system controller 62 provides the necessary
signals for paper transport, writing instrument 12 operations, and
the like as necessary for printer 10 operations. The carriage
scanning axis is conventionally designated the x-axis, the print
media transit axis is designated the y-axis, and the printhead
firing direction is designated the z-axis.
[0006] One source of image quality degradation is print head
crashes on the media surface. These crashes can be induced by the
media rising up off the main printing belt into the swept volume of
the printheads. The cause of the media buckling is usually due to
the wet colorant ink-jet printing process itself. As the fluid from
the ink droplets is absorbed by the paper fibers, regions of the
media expand differently as a function of the volume of ink in the
region. This is also referred to as "cockle," an irregular rather
than planar surface produced in paper by the saturation and drying
of ink deposits on the fibrous medium. As a sheet of paper gets
saturated with ink, the paper grows and buckles in a seemingly
random manner. Paper printed with images are more saturated with
colorant than simple text pages and thus exhibit great paper cockle
effects. Colors formed by mixing combinations of other color ink
drops form greater localized saturation areas and also exhibit
greater cockle tendencies.
[0007] One known solution for this problem is using a combination
of heat, vacuum, and airflow to dry the media quickly, holding it
down during the critical time just after ink deposition. However,
this drying of the ink can also cause problems in local
environmental conditions. Moreover, when media sits in a high
humidity environment, it absorbs water from the air and stores the
moisture in its fibrous structure, causing expansion. Therefore,
even pre-printing, paper moisture content is a significant problem.
Under common ambient atmospheric conditions (e.g., an office
environment having a relative humidity of about 80% at 30.degree.
C.), paper commonly used for ink-jet printing can have a water
content that is significant to the process. Depending on actual
humidity, the moisture content of paper can be from about 1% to
10%. If an expanded sheet is then brought into a high temperature
location, such as a heated print zone, the moisture in the fibers
will be driven out and the media again will try to shrink. If this
shrinkage is done abruptly to only a section of the media as
opposed to the entire sheet at once, shrink cockle results. This
can result in printhead crashes at raised regions.
[0008] Some types of print media heating techniques assigned to the
common assignee of the present invention provide such exemplary
prior art solutions:
[0009] U.S. Pat. No. 5,287,123 for a PRE-HEAT ROLLER FOR THERMAL
INK-JET PRINTER,
[0010] U.S. Pat. No. 5,329,295 for a PRINT ZONE HEATER SCREEN FOR
THERMAL INK-JET PRINTER,
[0011] U.S. Pat. No. 5,399,039 for an INK-JET PRINTER WITH PRECISE
PRINT ZONE MEDIA CONTROL,
[0012] U.S. Pat. No. 5,406,321 for a PAPER PRECONDITIONING HEATER
FOR INK-JET PRINTER,
[0013] U.S. Pat. No. 5,428,384 for a HEATER BLOWER SYSTEM IN A
COLOR INK-JET PRINTER,
[0014] U.S. Pat. No. 5,461,408 for a DUAL FEED PAPER PATH FOR
INK-JET PRINTER,
[0015] U.S. Pat. No. 5,467,119 for an INK-JET PRINTER WITH PRINT
HEATER HAVING VARIABLE HEAT ENERGY FOR DIFFERENT MEDIA,
[0016] U.S. Pat. No. 5,510,822 for an INK-JET PRINTER WITH HEATED
PRINT-ZONE, and
[0017] U.S. Pat. No. 5,668,584 for a METHOD OF MULTIPLE ZONE
HEATING OF INKJET MEDIA USING (A) SCREEN PLATEN.
[0018] In U.S. Pat. No. 5,742,315, Szlucha et al. describe a
SEGMENTED FLEXIBLE HEATER FOR DRYING A PRINT IMAGE. A segmented
flexible heater is disposed adjacently to a paper path for heating
before and during printing. In U.S. Pat. No. 5,896,154 for an INK
JET PRINTER, Mitani et al. describe a prior art belt type
preheating unit.
[0019] In vacuum belt paper transport subsystems, sometimes heat is
applied to the main belt with the vacuum being used to ensure
contact to a heater. During heating, the paper 16 is dried. As
moisture leaves the paper 16, the paper shrinks. This shrinkage is
a change in paper size that is not matched by an equivalent change
in the belt 32. Therefore, there will generally be relative motion
between the two when the shrinkage occurs as the paper 16 is being
transported by the belt 32 which can lead to dot placement
error.
[0020] In vacuum belt systems, "edge-scalloping" of the sheet is a
common occurrence. Edge-scalloping is generally a waviness
occurring along the edges of a sheet due to a difference in the
drying time from the central regions of the sheet, another form of
cockling as described above. Edge-scalloping is a result of
cockling effects compounded by irregular drying across the page
area. The difference in heat exchange between the heater and the
sheet is exacerbated in a vacuum transport system because vacuum
loss around the sheet edges can lead to a loss of contact with a
resultant loss of heat transfer. The interior regions of the sheet
can dry faster and shrink faster than the edge regions. The
resultant distortion is scalloped edges.
[0021] Actual shrinkage and other shape changes will of course be
dependent on actual moisture content and paper thickness. Thus,
preheating and print-zone heating of the paper can affect ultimate
print quality characteristics. Temperature control is yet another
factor which will be dependent on throughput time and media
type.
[0022] There is a need for improved techniques of print media
heating and flattening for a vacuum belt hard copy apparatus.
SUMMARY OF THE INVENTION
[0023] In its basic aspects, the present invention provides a
method for flattening print media prior to ink-jet printing
thereon, including the steps of: heating the print media over a
predetermined time and temperature such that moisture content is
substantially reduced prior to printing thereon; and pressing the
print media upstream of printing thereon.
[0024] In another basic aspect, the present invention provides a
print media preheating subsystem for an ink-jet hard copy
apparatus, having a belt-type print media transport means for
transporting print media via a vacuum belt along a media path
through a print zone of the apparatus, the preheating subsystem
including: upstream of the print zone, media transporting means for
transporting print media along the path toward the print zone, the
media transporting means including at least two complementary
contact devices wherein the print media has each face thereof in
contact with a respective device surface; and heating means for
heating at least one of the contact devices surface such that heat
is transferred to the print media therefrom.
[0025] In another basic aspect, the present invention provides a
method for preheating an ink-jet print medium sheet prior to
printing thereon in an ink-jet hard copy apparatus, including the
steps of: pressing the sheet between a pair of print media
transport devices in the print media transport path prior to
printing on the media; moving the sheet with the devices toward a
printing-zone of the apparatus; and heating a surface of at least
one device of the pair of devices such that heat is transferred to
the sheet substantially immediately prior to depositing ink
thereon.
[0026] In another basic aspect, the present invention provides an
ink-jet hard copy apparatus, including: an ink-jet writing
instrument positioned adjacently to a printing-zone in a print
media transport path of the apparatus; a vacuum belt subsystem for
receiving a sheet of print media, including a vacuum belt for
transporting the sheet through the printing-zone; and upstream of
the printing-zone, a preheating subsystem having a media transport
mechanism and a heater mechanism associated with the media
transport mechanism wherein heat is applied by the preheating
subsystem to at least one surface of the sheet prior to the sheet
entering the printing-zone and receiving colorant from the writing
instrument.
[0027] In another basic aspect, the present invention provides a
print media ironing device for ink-jet printers having a vacuum
transport belt for moving a sheet of print media through a
print-zone, including: at least one heater providing a
pre-shrinkage region wherein the sheet passing therethrough
experiences a substantial moisture content reduction; and at least
one ironing mechanism, downstream of said region, wherein the sheet
is pressed into a substantially planar configuration prior to
entering the print-zone.
[0028] Some advantages of the present invention are:
[0029] it provides improved heat transfer to print media;
[0030] it provides improved image quality;
[0031] it is scalable;
[0032] in one embodiment it can be used to eliminate the need for
vacuum upstream of the print-zone;
[0033] it provides a flat, stable media for printing;
[0034] it adds a holddown force for media types that are permeable
by the vacuum--induced air flow; and
[0035] it prevents loss of vacuum at edges of all media types.
[0036] The foregoing invention summary and list of advantages is
not intended by the inventors to be an inclusive list of all the
aspects, objects, advantages and features of the present invention
nor should any limitation on the scope of the invention be implied
therefrom. This Summary is provided in accordance with the mandate
of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the
public, and more especially those interested in the particular art
to which the invention relates, of the nature of the invention in
order to be of assistance in aiding ready understanding of the
patent in future searches. Other objects, features and advantages
of the present invention will become apparent upon consideration of
the following explanation and the accompanying drawings, in which
like reference designations represent like features throughout the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 (PRIOR ART) is a schematic illustration of an ink-jet
hard copy apparatus in an elevation view.
[0038] FIGS. 2A, 2B and 2C are schematic drawings of a first
embodiment of the present invention.
[0039] FIGS. 3A, 3B and 3C are schematic drawings of a second
embodiment of the present invention, employing three paper
transport belts.
[0040] FIG. 4 is a preferred embodiment of a two belt embodiment
the present invention.
[0041] FIG. 5 is an alternative embodiment employing a soft
material roller in conjunction with a main transport belt.
[0042] The drawings referred to in this specification should be
understood as not being drawn to scale except if specifically
noted.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] Reference is made now in detail to a specific embodiment of
the present invention, which illustrates the best mode presently
contemplated by the inventors for practicing the invention.
Alternative embodiments are also briefly described as
applicable.
[0044] FIGS. 2A, 2B, and 2C are schematic illustrations of a
two-belt embodiment of the print media preheating strategy of the
present invention. In FIG. 2A, upstream of the print-zone 34 along
the paper path 31, a heating device 201--such as a conductive
heater (although other known devices may be used in any specific
implementation as may be design expedient)--is positioned to heat a
pre-printing positional region of the vacuum belt 32. An upper,
endless-loop, transport belt 202 is positioned to provide a contact
force, pressing the sheets of paper received from the input pick
mechanism (not shown) between the two belts 32, 202. Both faces of
the paper are in intimate contact with a belt surface. There are
other known ways to force media against a heated platen, such as
with a weight or pressurized belt. However, when vacuum is present,
it is preferred to have only the belt 32 on the vacuum side
perforated to ensure that no vacuum is lost on the opposite, top,
side. The non-perforated belt is vacuumed against the perforated
belt, helping to press the medium therebetween. Therefore, it is
preferred to have heat and vacuum on the same side. It is also
preferred that the non-perforated belt 202 be wider than the widest
media selectable for a particular printer implementation. Vacuum
tapers off at the media edge, so by using a wider, non-perforated
belt 202, the vacuum on the media can be constant to the edges.
Moreover, the vacuum subsystem 37 can be used to transport water
vapor out of the printer 10.
[0045] FIG. 2B provides an implementation with a heater 201'
operative in conjunction with the upper transport belt 202, heating
the surface of the sheet which will receive ink in the print-zone
34, further reducing ink dry time and cockling of the sheet.
[0046] FIG. 2C provides and implementation with heater devices 201,
201' associated with both the vacuum belt 32 and the upper pressure
belt 202. Note that this has an advantage for drying thicker media
as heat is now applied to both sides.
[0047] The options of adding heat to one or both sides of the media
can also optionally use vacuum or another known manner exhaust
subsystem in the preheat zone (see description of FIG. 3C below).
If only one heater is used, adding vacuum to the same side of the
media that has the heating improves the heat transfer capability by
reducing the thermal resistance. A temperature range of
approximately 135.degree. C..+-.15.degree. has been employed, but a
specific implementation may use a different range depending on the
type of media used in the hard copy apparatus. Note that both belts
may be driven, or the upper transport belt 202 may simply be idler
mounted and driven by friction; a variety of implementations as
would be known in the art can be employed.
[0048] FIGS. 3A, 3B and 3C illustrate implementations of a three
belt ink-jet printer system embodiment in accordance with the
present invention. To the standard vacuum belt-type printer
system--such as detailed in FIG. 1 and represented here
schematically as print-zone subsystem 10'--a second, belt-type,
print media preheat subsystem 310 is provided in the paper path 31
upstream of the print-zone subsystem. The preheat subsystem 310 has
two belts 302, 303, at least one of which has a heater 301 device
(see also heater element 301', FIG. 3C) associated with it as shown
in various combinations by these three FIGURES. In a one heated
belt implementation such as in FIGS. 3A and 3B, the unheated belt
is used to provide contact force. Heating both belts such as in
FIG. 3C provides the improved heat transfer advantages as described
with respect to FIGS. 2A-2C.
[0049] FIG. 3C also demonstrates the option of providing vacuum to
the preheat zone between the preheater subsystem 310 belts 302, 303
to assist with vapor removal and to improve heat transfer. Note
that another embodiment such as depicted in FIGS. 3A and 3B but
similarly employing vacuum with one of the belts 302, 303 is
another option.
[0050] By separating the preheating subsystem 310 from the
print-zone subsystem 10', relative motion between belts and media
as described in the Background section is restricted to the
preheating subsystem 310. In this construct, the separate subsystem
10', 310 belts can be run at different speeds based on throughput
specifications to improve overall performance.
[0051] A pinch roller 42 (also in FIG. 1), positioned at the paper
path 31 upstream entrance to the main vacuum belt 32 to square the
media sheet, removing or at the least reducing, any skew before the
leading edge enters the print-zone 34, can be used in conjunction
with the present invention as described in further detail in
assignee's U.S. patent application Ser. No. 09/______ (attorney
docket no. 10991882-1) by Wotton et al. on Apr. 3, 2000, for
Linefeed Control in Belt-Type Printers (incorporated herein by
reference).
[0052] The preheat subsystem 310 provides the advantage of running
the preheater at intermittent speeds or continuous speed (versus
ink-jet swath printing using stepped media advance). A buckling of
the media between the preheat subsystem 310 and the downstream
combination of the roller 42 and vacuum belt 32 can be allowed. In
other words, a predetermined degree of buckling of the media is
induced along the print media path between the upstream, heated
transport mechanisms and the downstream point of contact with the
vacuum belt. The preheating system 310 can be run at a different
speed, including in continuous motion. This provides advantageous
design options for implementing the present invention.
[0053] Again, the preheat subsystem 310 belts 302, 303 can be
perforated to allow water vapor to escape. In a vacuum belt
construct, as shown in each embodiment, again it is preferable that
only one belt would be perforated so that the vacuum will pull
against the other belt, providing vacuum-assisted pressing of the
medium therebetween.
[0054] FIG. 4 shows a seventh embodiment of an ink-jet printing
system 400. It has been found that pre-heating a sheet of paper
having a significant moisture contact before sandwiching, or
"ironing," it between belts 32, 202 upstream of the print-zone will
drive out a majority of the moisture prior to the sheet being
captured by the nip formed between the belts. Most of the shrinkage
will occur in this unconstrained sheet of paper "pre-shrink region"
of the system 400. Width shrinkage (across the grain of the paper
fibers) as much a 1.5% (three-millimeters in a 216-mm wide paper)
has been observed; with the grain, shrinkage is approximately 50%
the cross-grain amount. Use of a pre-shrink region reduces
shrinkage during the actual ironing between the belts 32, 202 which
otherwise could result in wrinkles, buckles, and folds in the paper
sheet before it ever reaches the print-zone 34. It will be
recognized by those skilled in the art that the time of contact
between the sheet and heater 201 in the preshrink region of the
system 400 will depend on the throughput of the implementation. A
heated pre-shrink region of about 50 to 60 millimeters in the paper
path 31 upstream of the nip between the belts 32, 202 should be
adequate for most throughput speeds common to state of the art for
print swaths of one-inch height or less.
[0055] FIG. 5 shows another embodiment similar to the embodiment of
FIG. 2A. However, the belt 202 has been replaced with a
soft-material roller 501. The roller 501 is slightly greater in
width than the largest paper width used in the system 500. The
sheet of paper in the paper path 31 will cross a heated pre-shrink
region 503 (as explained in conjunction with the embodiment of FIG.
4) upstream of a capture nip between the belt 32 and roller 501
outer surface. Passing the sheet thereafter at temperature, under
pressure, for a period of time, through the contact area of the
belt 32 and roller 501 will iron the sheet just prior to its
entering the print-zone 34. Preferably, a relatively soft material
such as cellular silicone foam should be employed for the roller
501, or at least its outermost layer to increase this contact area.
A material with a durometer number (Shore A) in the range of twenty
to sixty has been successfully employed. For common
state-of-the-art ink-jet printers, a contact area of about 10
millimeters in the paper path direction has been found to provide
adequate ironing of the sheet upstream of the print-zone 34. A
pressure in the contact area in the range of about
6-to-15-inches-of water can be employed. It will be recognized by
those skilled in the art that a specific implementation's
specifications will be a function of temperature and pressure
employed. Note that the concept of this embodiment can be extended
to provide two rollers as the pressing mechanism.
[0056] In summary, the present invention provides a print media
preheating method and apparatus that uses heat, vacuum, and
mechanisms in combination for drying and flattening a sheet prior
to ink-jet printing thereon. Pre-shrinking the media, driving out
and substantially reducing inherent moisture content prior to
depositing wet ink thereon provides greater flatness in the
print-zone whereby ink-jet print quality is improved.
[0057] The foregoing description of the preferred embodiment of the
present invention has been presented for purposes of illustration
and description. It is not intended to be exhaustive or to limit
the invention to the precise form or to exemplary embodiments
disclosed. Obviously, many modifications and variations will be
apparent to practitioners skilled in this art; for example, while
conductive heat type devices are illustrated, radiant heat devices
or the like might be employed. Similarly, any process steps
described might be interchangeable with other steps in order to
achieve the same result. The embodiment was chosen and described in
order to best explain the principles of the invention and its best
mode practical application, thereby to enable others skilled in the
art to understand the invention for various embodiments and with
various modifications as are suited to the particular use or
implementation contemplated. It is intended that the scope of the
invention be defined by the claims appended hereto and their
equivalents. Reference to an element in the singular is not
intended to mean "one and only one" unless explicitly so stated,
but rather means "one or more." Moreover, no element, component,
nor method step in the present disclosure is intended to be
dedicated to the public regardless of whether the element,
component, or method step is explicitly recited in the following
claims. No claim element herein is to be construed under the
provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the
element is expressly recited using the phrase "means for . . .
"
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